It has long been known that non-protein nitrogen (NPN) can be incorporated into feed for ruminant animals as a substitute for protein sources. The most common source of NPN for ruminant animal feed is urea. Urea can be digested by ruminant animals and converted into bacterial protein by ureases present in the rumen of the animal. The bacterial protein is in turn liberated and used by the animal after the bacteria leave the rumen and enter the small intestine of the animal.
Intermediate steps in this process include the conversion of urea to ammonia and the conversion of ammonia to amino acids. The conversion of urea to ammonia in the rumen occurs more rapidly than the conversion of ammonia to amino acids. If ammonia is generated too rapidly in the rumen, not all of the ammonia will be converted to amino acids, thus resulting in wastage of some of the nutrient value of the urea. Moreover, excess ammonia may be released into the bloodstream of the rumen, causing alkalosis and possibly illness or death of the animal.
The prior art has recognized that these problems may be alleviated if the urea in the ruminant feed is released, i.e., made bioavailable to ureases in the rumen, at a controlled rate approximately equal to or less than the rate of conversion of ammonia to protein. U.S. Pat. Nos. 3,934,041, 4,035,479, 4,109,019, and 4,994,284 discuss these and other advantages of slow urea release from ruminant feeds. In keeping with this understanding, the prior art has provided several attempts to provide ruminant feeds that allow NPN from urea or other sources to be released at a controlled rate. Examples of such attempts are described, for example, in U.S. Pat. Nos. 3,940,493, 4,044,156, and 4,232,046.
Many of these prior art attempts are somewhat unsatisfactory. For example, U.S. Pat. No. 4,044,156 discloses urease-resistant glucosyl ureides for ruminant feeds. The ureides are prepared when glucose and urea react under acidic drying conditions. While these ureides allow urea to be released at a controlled rate, the nutritive value of the ureides is limited. Similarly, U.S. Pat. No. 3,934,041 provides a method for binding urea to an aldehyde using molasses. While the aldehyde-bound urea is nutritive, the nutritive value of the other components in the feed material is limited.
It is a general object of the invention to provide an NPN delivery system for a ruminant animal. It is another general object of the invention to provide a method for preparing an NPN delivery system for a ruminant animal.